As used herein, a dynamic image is a recording that includes multiple separate images viewable from separate angles. Dynamic image can also include a recording of an optical element such as a lens or filter that exhibits different angular and intensity light modulations at different locations on the recording. A dynamic image may produce a motion image that is viewed by moving the angle of viewing to see a succession of image frames in a motion image sequence. A dynamic image can produce a depth image if each eye of a viewer receives different images of a stereo pair of images. Alternatively, a dynamic image may display a plurality of unrelated images viewable from different angles.
Holography has been used for generating dynamic images. The original method for making a white light hologram involved splitting a coherent light beam into two beams and illuminating an object with one of the beams. The scattered light from the object was then interfered with the second beam from opposite sides of a recording medium. To interfere the light, the beams must cover the same size. These size constraints and the need for the object to be illuminated has prevented the widespread use of holographic imaging. Various holographic recording media such as chromated gelatin, a photosensitive polymer-monomer mix, or a silver halide emulsion are known in the art.
One method of making a dynamic image hologram is disclosed in Personalized Hologram, by Kihara et al., IS&T's 2001 PICS Conference Proceedings, pp. 22-25. U.S. Pat. No. 5,949,559 issued Sep. 7, 1999 to Kihara et al. further describes a printer apparatus and method for making the dynamic image holograms. The data for driving the printer is generated as described in U.S. Pat. No. 6,377,371 issued Apr. 23, 2002 to Baba et al.
The process disclosed by Kihara et al. is shown in FIG. 1. A laser beam 30 from laser 10 is reflected from mirror 20, and split into two beams with beam splitter 40. The beams are made uniform with a spatial filter 50. One of the beams is focused through cylindrical lens 60 to a line which impinges on the holographic recording medium 90. The holographic recording medium 90 is attached to a linear translation stage 100 which allows the medium to be moved perpendicular to the long axis of the cylindrical lens 60 while maintaining focus. The other beam on the obverse side of the holographic recording medium 90 is collimated, passed through the pixilated light modulator 70, and focused to a line with cylindrical lens 60. The pixilated light modulator 70 is controlled by computer 110, which includes processing electronics for modulating individual pixels of the pixilated light modulator. The focused line from the beam which passed through the pixellated light modulator 70, hereafter called the object beam 44, is focused on a diffuser 80 which is in close proximity to the focused line of light from the obverse side, hereafter called the reference beam 42. The light from the two lines of focused light interfere and the holographic recording medium 90 records that information for all the angles around that line. The holographic recording medium 90 is translated and the process is repeated for the next line until complete.
The holographic recording medium 90 is developed or otherwise processed to generate an interference pattern which can be viewed. To view the images, an incoherent light source irradiates the medium from nearly the same angle as the reference beam's angle to the medium and the diffracted light can then be observed by a viewer.
One of the problems encountered by Kihara et al. was generating a uniform beam; in U.S. Pat. No. 6,185,018 issued Feb. 6, 2001, they describe using condensing lenses, lenslet arrays, and lenticular arrays with a rod type light integrator to give a uniform object beam. In a typical white light line hologram, the hologram is written a line at a time. White light refers to the type of hologram which has the reference on the opposite side from an object beam, it is referred to as a white light hologram because it is viewable under white incoherent light. The object beam has information encoded into it by reflecting off an object or being passed through or off a pixilated light modulator. The pixilated light modulator is a device which changes the light in an incident beam spatially. An LCD display is an example of a pixilated light modulator since it changes the light passing through it on a pixel by pixel basis (spatially changes it). The focusing of the modulated object beam to a line turns pixels in the focus direction into pixel information coming out at an angle as shown in FIG. 1. In the perpendicular direction, the cylindrical lens used to focus to a line has no power and so the pixels in that direction correspond to an image line.
To generate a line hologram image, a line is written which contains one line of image for each image desired wherein each different image line is projected at a different angle. To generate the complete images, the process is repeated to form a complete image at different angles. Some consideration is necessary of the viewing distance because if a close view distance is desired, the angles for a specific images line will have to vary from the top to the bottom of the media to ensure the viewer's eye receives only the one image.
In the case of a full hologram, instead of using a cylindrical lens to focus to a line, a regular lens is used to focus to a point. In this case, all pixels on the modulator correspond to different angles and a single pixel from an image. This yields a full holographic reproduction from all angles but since the image is written a point at a time, the time to write a line can be substantial.
There is a need therefore for an improved method of making holographic images that avoids the problems noted above.